Studies On Preparation Of High Purity Magnesia From Bischofite In QingHai Salt Lakes

There are extremely abundant of bischofite resources existing in Qinghai salt lakes of our country, but for a long time they did not get enough use. Because of the technological problems to be resolved, they are discharged as a waste in the production of potassium fertilizer, resulting in a huge waste of resources and brought serious environment pollution. The exploitation of them becomes urgent mission.For a solution to these problems, extensive studies on preparation of high purity magnesia have been carried out in the paper. We selected bischofite in ChaErHan as raw material and placed emphasis on the studies of the preparation process based on ammonia method, some key problems were resolved which would greatly lower the production cost. The MgO content reaches 99.5%, and apparent density reaches 3.55g/cm³ using the new production process flow. A new preparation method of high purity magnesia has been successfully developed which will greatly alleviates the environment pollution and will turns the waste into a valuable product if being industrialized.Traditional ammonia method has many problems in filtration of Mg(OH)₂ soliquoid and its purity, for a long time they were not well resolved. Generally the water percentage of Mg(OH)₂ precursor reaches 30-40% and its quality is inferior than high grade Mg(OH)₂ quality standard. Different from the traditional ammonia method, we think that the generation and the growth environment of Mg(OH)₂ crystal in depositing reaction system show great effects on filtration of Mg(OH)₂ deposit. The paper brought forward a new process using the recombination effect of the buffer system and the crystal particle action, which evidently improved the filtration of Mg(OH)₂ soliquoid. The Mg(OH)₂ product in the new ammonia method has properties superior than that of the traditional one: lower water content (<15%) and higher purity.Intensified studies were carried out on thermo-decomposition kinetic mechanism of Mg(OH)₂, we think that the thermo-decomposition of Mg(OH)₂ is a complex process and the whole decomposition process cannot be represented by only one mechanism function. The process can be divided into two parts and two mechanism functions can represent it, the dividing temperature is 397℃. The nucleation mechanism can represent kinetic control type before this temperature, and kinetic model is A3, while after this temperature the kinetic control type is diffusion control, the kinetic model is the famous Ginstling-Broustein model(D4). We also improved Freeman-Carroll method, a method used to calculate the solid state thermo-decomposition kinetic parameters which usually has problems in accuracy. We resolved the problems by improving the differential equation of conversion degree α . The activation energy 'E' is 122kJ/mol, the value of reaction order 'n' is 0.68 by the improved method.